1. Field of the Invention
This invention relates to a method and a means for extinguishing fires utilizing a non-pressurized device and a dry chemical.
2. Description of Related Art
Fire extinguishing agents may very well be one of the most significant safety devices commonly employed by modern man. As the Kirk Othmer Encyclopedia of Chemical Technology (3 ed., 1984) notes "[c]ontrol and extinguishment of fire has always been a human concern. Water was the first agent to be used; however, the need for agents other than water became apparent as the industries of civilization introduced new and more combustible fire materials. Plastics, chemicals, petroleum products, and combustible metals have become daily fire hazards that have to be dealt with by agents other than water."
The combustion process has four basic prerequisites heat; fuel; oxidizing agent; and suitable chemical-reaction path. Thus, inhibiting a combustion process must involve one or more of the following: remove heat at a faster rate than it is released; separate the fuel and the oxidizing agent; dilute the vapor phase concentration of fuel and oxidizing agent below that which is necessary for combustion; and terminate the chain-reaction sequence.
From a practical standpoint these inhibitory processes are carried out by a variety of commonly employed extinguishants. For example, water and carbon dioxide act by exerting a cooling effect. carbon dioxide additionally acts by diluting or inerting the available oxygen. Separation of fuel from the air (oxygen) is usually achieved by the foams, although since carbon dioxide and the halogenated hydrocarbon gasses (Halons) are heavier than air, they, too, can form a barrier between the fuel and air.
The ability of the Halons and dry chemicals to extinguish fires cannot be completely explained by the above concepts, however. It is felt that their action is owing more to disruption of the chain reaction. Although the mechanism of reaction is not completely understood, there have been a number of possibilities proposed.
Nonetheless, dry-chemical extinguishants similar to the present invention, have been known and used for some time. Sodium bicarbonate, perhaps the original dry-chemical fire extinguishant, found widespread use as early as the Civil War. Today, the most commonly used chemical bases for dry-chemical extinguishants are sodium bicarbonate, potassium bicarbonate, potassium carbonate, monoammonium phosphate, and potassium chloride.
Early use of pressurized fire extinguishers containing a dry-chemical extinguishant appeared around 1913. These extinguishers suffered, however, from picking up moisture and ensuing caking problems. Subsequent formulations have improved the free-flowing nature of the extinguishant by coating it with magnesium stearate and more recently, the use of silicones. Silicones have not only proved helpful as a moisture-proof barrier but also improved the flow characteristics of the agent and imparted a higher degree of heat resistance to the extinguishant.
Most dry chemicals are ground to a particle distribution between 5-108 .mu.m, most have a median particle size of about 20-30 .mu.m. All existing agents contain additives that make them water repellant, less hygroscopic, and more flowable with a reduced tendency toward packing.
Despite such advances and modifications in the art of fire extinguisher design and extinguishant formulation, there remained to be developed a multipurpose, effectively fail-safe extinguisher. More specifically, the present invention has arisen due to the absence in the art of a non-pressurized version of a dry-chemical fire extinguisher which is capable of meeting basic safety and effectiveness requirements, such as would be indicated by an underwriter's approval, such as Applied Research Laboratories.
Monoammonium phosphate (MAP), while generally considered to be among the dry-chemical extinguishants, is also the base chemical used in something known as a multipurpose agent, and also known as all-use, all-purpose, and ABC agents.
The term "ABC agent" derives from the fact that fire extinguishing agents and equipment are classified by the National Fire Protection Association (NFPA) into four categories. The classes of fire relevant to the instant invention are as follows:
Class A fires are fires in ordinary combustible material, eg., wood, cloth, paper, rubber, and many plastics. PA1 Class B fires are fires in flammable and combustible liquids, gases, and greases. PA1 Class C fires are fires that involve energized electrical equipment where the electrical nonconductivity of the extinguishing media is of importance. (When electrical equipment is de-energized, extinguishers for Class A or B fires may be used safely.)
Most of the presently approved dry-chemical fire extinguishers are pressurized canisters which rely on an internal highly pressurized gas for expulsion of the extinguishant. The problem which arises, however, is that eventually the pressurized canister loses the necessary pressure and thus the extinguisher has a limited shelf-life and a need for maintenance. Without such maintenance these extinguishers present the dangers of malfunction and imbue the potential user with a false sense of security.
Additionally, because of the pressure that these canisters must necessarily withstand, the canisters are constructed of decidedly opaque materials. The opacity of such canisters prevents the user from even vaguely gauging the amount of extinguishant remaining at any given time, and especially either before or after use. Again, the possibilities of malfunction, nonfunction and a false sense of security present life-threatening dangers.